JP5876563B1 - Welding material for cast steel parts - Google Patents

Abstract

A welding material for reliably repairing a crack generated in a cast steel member on site is provided. The main component is nickel and chromium is contained in an amount of 0.8% to 5.5% by weight. It may contain 0.03% to 0.08% by weight of carbon. Silicon may be included in an amount of 0.4 wt% to 0.8 wt%, and manganese may be included in an amount of 0.7 wt% to 1.3 wt%. Each of phosphorus and sulfur may be contained in an amount of 0.01% by weight or less. [Selection] Figure 2

Description

  The present invention relates to a welding material used for repairing a crack generated in a cast steel member.

  Cast steel members such as steam turbine casings and valves provided in power plant facilities are subject to thermal stress when starting and stopping, which may cause cracks mainly.

  When such a crack occurs in a cast steel member, conventionally, the portion has been ground and removed. However, when the thickness of the cast steel member after grinding and removing the crack becomes thinner than the required minimum thickness, the cast steel member becomes unusable and must be replaced with a new one. Therefore, after the grinding and removal, overlay welding of the portion with a welding material is also performed.

  As a method of build-up welding, for example, in Patent Document 1, as a welding material for hardening build-up that is hardened by supercooling treatment after welding build-up on a cast iron base material, the basic component composition of the material is weld-filled And satisfying the Ni equivalent and Cr equivalent contained in the region of the Schaeffler's organization chart, the hardness difference before and after the supercooling treatment is equal to or greater than a predetermined value, and the martensitic transformation start temperature is set to be equal to or lower than the predetermined temperature Have been described.

Japanese Patent Laid-Open No. 8-141783

  However, since many cast steel members in the power plant facilities as described above are large and cannot be taken back to the factory to perform welding work, the welding must be performed on site. However, it is difficult to control the temperature of the welded part at the site, and the welded part may be rapidly cooled to cause cracks.

  This invention is made | formed in view of said point, The objective is to provide the welding material for repairing the crack which generate | occur | produced in the cast steel member on-site reliably.

The present invention for achieving the above-mentioned object is a welding material used for repairing a crack generated in a cast steel member, comprising nickel as a main component and components other than nickel as 0.8 wt% to 5. It contains only 5% by weight of chromium and impurities, and does not contain iron .

As in the present invention, the main component of the welding material is nickel, which has a low cooling rate even if the cooling rate is high, thereby facilitating temperature control and temperature control during pre-heat treatment and post-weld heat treatment during welding. It is possible to facilitate welding. It is also possible to eliminate the need for pre-heat treatment during welding.
In the present invention, chromium is added to nickel. Since nickel is easily oxidized and corroded at high temperatures, the addition of chromium can improve the oxidation resistance and corrosion resistance. However, since chromium has a property of hardening the welded portion, if the amount of chromium added is large, there is a risk that cracking due to thermal stress will occur again after repair. Therefore, in the present invention, the addition ratio of chromium is minimized to 0.8% to 5.5% by weight, thereby ensuring the oxidation resistance and corrosion resistance of the repaired part without causing the recurrence of cracks after repair. Can be improved.

  Thus, according to the welding material of the cast steel member of the present invention, a crack generated in the cast steel member can be reliably repaired on site.

  In the present invention, carbon may be contained in an amount of 0.03% to 0.08% by weight. . Thereby, the strength of the welded part after repair can be improved.

  In the present invention, silicon may be contained in an amount of 0.4 wt% to 0.8 wt%, and manganese may be contained in an amount of 0.7 wt% to 1.3 wt%. As a result, it can be combined with the base material and oxygen in the atmosphere to prevent oxygen from becoming a cavity defect.

In the present invention, the contents of phosphorus and sulfur as impurities may be 0.01% by weight or less , respectively. Thereby, embrittlement of a welding member can be prevented.

  According to the present invention, a crack generated in a cast steel member can be reliably repaired on site.

It is a figure which shows the outer shell member 10 of a steam turbine casing. It is a figure explaining the characteristic of the component of the welding material of this embodiment. It is the figure which showed the example of the component of the welding member of this embodiment. It is a flowchart explaining the repair method of the outer shell member 10 by the welding member of this embodiment. It is a figure explaining the process of cutting the crack 12 and forming a recessed part. It is a figure explaining the process of carrying out overlay welding of the recessed part 13 using a welding member.

The welding material which concerns on this embodiment is demonstrated.
FIG. 1 shows an outer shell member 10 of a steam turbine casing provided in a thermal power plant or a nuclear power plant. The outer shell member 10 is made of, for example, CrMo cast steel or the like, and receives thermal stress as it starts and stops. As a result, the outer shell member 10 is subjected to creep damage, and a crack 12 is generated on the inner surface 11 thereof. Hereinafter, the welding material of the cast steel member of the present embodiment will be described by taking the case of repairing the crack 12 as an example.

  FIG. 2 is a diagram for explaining the characteristics of the components of the welding material of the present embodiment. As shown in the figure, the welding material of the present embodiment is an alloy containing nickel as a main component. Nickel is hard to cure even if the cooling rate is high, so by using nickel as the main component, temperature control and temperature control in pre-heat treatment and post-weld heat treatment (PWHT) are easy. As a result, on-site welding can be facilitated.

  Moreover, this welding material contains chromium (Cr), carbon (C), silicon (Si), manganese (Mn), and chromium (Cr).

  Since nickel described above has a property of being easily oxidized and corroded at a high temperature, the addition of chromium can improve the oxidation resistance and corrosion resistance. On the other hand, since chromium has a property of hardening the welded portion, if the amount of chromium added is too large, cracking due to thermal stress is likely to occur after repairing. Therefore, in the welding material of this embodiment, the addition ratio of chromium is minimized to about 1 to 5% by weight. More specifically, the addition ratio of chromium is set to 0.8 to 5.5% by weight. In this way, by minimizing the amount of chromium added, the oxidation resistance and corrosion resistance of the repaired portion can be reliably improved without causing the recurrence of cracks after repair.

  Moreover, as shown in FIG. 2, the welding material of this embodiment does not contain iron (Fe). This is due to the following reasons. Usually, it is considered effective to add iron in order to increase the strength of the weld. However, when welding is performed on a cast steel member, a part of iron which is a main component of a base cast steel member (for example, Cr-Mo cast steel) is mixed in the welded portion. For this reason, in the welding material of the present embodiment containing nickel as a main component, the strength of the welded portion can be sufficiently maintained by the iron component mixed during the welding. Therefore, in the welding material of this embodiment, iron is not added intentionally. This is because the strength of the welded portion can be sufficiently increased without adding iron to the welding material in advance.

  Moreover, in the welding member of this embodiment, the addition ratio of phosphorus (P) and sulfur (S) is 0.01% by weight or less, respectively. Since impurities such as phosphorus and sulfur may cause the welded member to become brittle, the content ratio of these components is minimized by high-temperature treatment or the like.

  FIG. 3 is a diagram showing an example of components of the welding member of the present embodiment.

  As shown in the figure, in the case 1 welded member, the addition ratio of carbon is 0.05 wt% (hereinafter, “%” means wt%), silicon is 0.6%, manganese is 1.0%, chromium is 1.0%, and the balance is nickel. However, in actual blending, carbon is 0.03 to 0.08%, silicon is 0.4% to 0.8%, manganese is 0.7 to 1.3%, and chromium is 0.8% to 1%. If there is an addition ratio in the range of 2%, it shall be allowed as an error.

  In the case 2 welded member, the addition ratio of carbon is 0.05%, silicon is 0.6%, manganese is 1.0%, chromium is 5.0%, and the balance is nickel. However, in actual preparation, carbon is 0.03 to 0.08%, silicon is 0.4% to 0.8%, manganese is 0.7 to 1.3%, and chromium is 4.5% to 5%. Any addition ratio in the range of 5% is allowed as an error.

  Next, the repair method of the outer shell member 10 using such a welding member will be described. FIG. 4 is a flowchart for explaining an example of a repair method for the outer shell member 10.

  As shown in the figure, first, a crack 12 generated in the outer shell member 10 and its periphery are cut to form a recess (S1). For example, FIG. 5 is a cross-sectional view of the outer shell member 10 in the thickness direction, but the surface 11 of the outer shell member 10 is cut so as to include all the cracks 12 to form the recesses 13.

  Next, the formed recess 13 and its periphery are preheated to about 200 ° C. to 300 ° C. with a burner or an electric heater, for example (S2 in FIG. 2). However, since the welding member of the present embodiment is mainly composed of nickel which is hard to cure even if the cooling rate is fast, this preheating may not be performed. Even when preheating is performed, temperature adjustment is easy.

  Next, build-up welding of the recessed part 13 is carried out using a welding member (S3). For example, as shown in FIG. 6, a welding member is introduced into the recess 13 using a welding rod by covering arc welding to form the built-up portion 14.

  In this build-up welding, the iron content of the base metal is leached from the vicinity of the recess 13 by heating and enters the build-up portion 14 (reference numeral 16). As described above, iron is not added to the welded member, but the strength of the welded portion increases due to the intruding iron.

  Finally, a post-weld heat treatment is performed on the welded portion that has undergone overlay welding (S4 in FIG. 2). Specifically, the build-up portion 14 and its surroundings are heated and held at about 700 ° C. with a burner or an electric heater, for example, and then gradually cooled.

  By this post-welding heat treatment, the residual stress in the welded portion is removed. Furthermore, since the welding member of the present embodiment is mainly composed of nickel that is hard to cure even when the cooling rate is high, the stress load on the welded portion accompanying cooling can be effectively suppressed. Therefore, it is easier to adjust the temperature of the welded part than the normal post-weld heat treatment.

As described above, the welding material of the cast steel member of the present embodiment is mainly composed of nickel that is hard to cure even if the cooling rate is high. Therefore, temperature adjustment and temperature management in pre-heat treatment and post-weld heat treatment are facilitated. This makes it easy to perform welding on site. In addition, since chromium is added to the welding material at a minimum (0.8% to 5.5%), the oxidation resistance and corrosion resistance of the repaired portion can be improved without recurring cracks after the repair. .
Thus, according to the welding material of this embodiment, the crack which generate | occur | produced in the cast steel member can be reliably repaired on-site.

  In addition, the description of the above embodiment is for facilitating understanding of the present invention, and does not limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and the present invention includes equivalents thereof.

10 Outer shell member, 11 Surface, 12 Crack, 13 Recess, 14 Overlay

Claims (4)

A welding material used to repair a crack generated in a cast steel member,
A welding material for a cast steel member comprising nickel as a main component and containing only 0.8 wt% to 5.5 wt% of chromium and impurities as components other than nickel and not containing iron . A welding material used to repair a crack generated in a cast steel member,
Contains nickel as its main component , and contains only 0.8 wt% to 5.5 wt% chromium, 0.03 wt% to 0.08 wt% carbon , and impurities as components other than nickel , and no iron A welding material for cast steel members. A welding material used to repair a crack generated in a cast steel member,
Nickel as a main component, and as components other than nickel , 0.8 wt% to 5.5 wt% chromium, 0.03 wt% to 0.08 wt% carbon, 0.4 wt% to 0.8 wt% Material for welding a cast steel member, which contains only 1 % by weight of silicon, 0.7% by weight to 1.3% by weight of manganese , and impurities, and does not contain iron . Welding materials of which the wherein the content of phosphorus and sulfur are impurities is 0.01 wt% or less, respectively, cast steel member according to any one of claims 1 to 3.

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